I haven't been following threads recently (too busy) but I do have a mildly
interesting result to report in re: split planes.

After discussions with our EMI experts we decided to do two different stack
ups with the same gerber files. This is a 10 layer/50 ohm board with
s-g-s-s-g-pslit-psplit-s-g-s, and the alternative was
s-g-s-psplit-g-psplit-s-g-s.

The first stack optimized for signal return path (only one signal layer sees
the power split, and layer 8 was routed carefully) while the second
optimized for VDD decoupling to ground.

Even though this was as controlled an experiment for EMI as we could do, the
specifics of the situation determine whether the result would be applicable
in general. We didn't have the luxury of trying to reroute layer 3 to be
better behaved across the new plane splits it sees in the alternate stack,
for example.

We found the first stack was a few dB better pretty much across the board.

Dennis Yarak

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